CAN bus data: accuracy and regulations

Not all CAN bus data is the same

You read everywhere that reading CAN-bus data makes your fleet smarter. That’s true. But there’s one question that’s missing from almost every sales brochure—and it’s the very thing that makes the difference between a dashboard you just look at and one you dare to drive by: where does that data actually come from?

Two systems may both display fuel consumption, mileage, or idle time, yet the source of those figures varies greatly. Some values are read directly from the vehicle’s systems via CAN bus or FMS. Others are calculated based on GPS distance, engine runtime, or standard consumption models. On the screen, the figures appear identical, but for analysis, reporting, and policy decisions, that source makes a world of difference.

It’s important to clarify right away: a calculated value does not mean that the supplier is substandard. Often, the cause lies elsewhere—the vehicle manufacturer does not release certain CAN data, the vehicle interface is not supported, there is no FMS connection, or the customer deliberately chose a simple GPS solution without a CAN connection. These calculated values are perfectly useful for identifying general trends; they are simply less suitable for precise control. Conversely, even CAN data isn’t always 100% “the truth”: the on-board computer also sometimes uses calculations, filtering, and rounding. But generally speaking, data read directly from the vehicle is indeed much more accurate than an external estimate based on GPS.

Calculated Data vs. Read Data: The Difference in Your Portfolio

Suppose you want to know how much fuel a delivery van actually consumes. There are roughly two ways a system can display that figure on your screen—and the difference isn’t whether one is “good” or “bad,” but rather where the value comes from and what you can use it for.

Anyone who wants to tackle idling needs figures that measure idling fuel consumption, not average it out. Anyone who wants to coach a driver on driving style won’t get very far with a derived average. And anyone who wants to detect waste or even fuel theft needs precisely that discrepancy between refueled and consumed fuel —a discrepancy that a calculated figure often smooths over. For fuel analysis, driving style coaching, CO₂ reporting, and maintenance planning, the source of the data therefore makes a big difference.

The insidious example: the odometer reading

For fleets with rotating drivers and heavy use, you want the actual mileage —not the theoretical mileage, not an “estimate.” If you schedule maintenance based on an estimated odometer reading, you’ll go wrong in two ways: you’ll bring vehicles in too early (unnecessary costs, downtime) or too late (accelerated wear and tear, warranty risk, breakdowns on the road). The same applies to warning lights on the dashboard: a system that reports the actual fault codes (DTCs) alerts you before damage occurs.

Why Some CAN Bus Data Is More Accurate Than Others

"CAN bus" is not a quality certification. It simply indicates that a system interfaces with the vehicle's internal network; it does not indicate how well it does so. The differences lie in the details, which are rarely listed on the product page:

• Which parameters are actually read? Some systems only capture the easy, widely available values. Others also read brand- and model-specific parameters—operating hours, PTO usage, AdBlue level, and engine load.
• How comprehensive is the vehicle coverage? A fleet is rarely uniform: different makes, model years, trucks, vans, and machinery. A system is only as strong as the range of vehicles it supports properly.
• How often and how consistently are measurements taken? Sporadic or erratic readings create gaps in your data—and those gaps are filled in with estimates.
• Is raw data being converted into reliable insights? The key lies in translating that data into numbers you can actually use to guide your decisions, without any noise.

Cheap options seem appealing until you realize that half your fleet isn’t providing any data or that the numbers don’t match your gas receipts. Accuracy isn’t a luxury—it’s a prerequisite for being able to use the data at all.

And then there's the legislation: now data can't be "approximate"

As long as data is used only to inform your internal decisions, a minor error is just a nuisance. But as soon as a regulatory body is looking over your shoulder, it’s a different story. Then “approximate” is no longer an option—you have to be able to prove it.

Tachograph: A Much Larger Group Starting July 1, 2026

Starting July 1, 2026, the tachograph requirement will also apply to delivery vans (and combinations) with a maximum authorized mass of 2.5 metric tons or more that engage in international freight transport or cabotage. For these vehicles, the European rules on driving and rest times apply, and a smart tachograph is mandatory. For purely domestic transport, the old 3.5-metric-ton threshold remains in effect—but during an inspection, your interpretation won’t count: you must be able to provide proper proof.

This is where the CAN bus comes in: accurate CAN bus data on load weight and usage helps you determine whether a vehicle consistently remains below the 2.5-metric-ton limit or falls just within the scope. And you must periodically and correctly download and store the tachograph data itself. You can’t build a file that will stand up to an audit using calculated or incomplete data—but you can with exact data read directly from the system.

Hours of Operation and Driving/Rest Times: Accurate Record-Keeping

• Machine operating hours form the basis for maintenance, rental invoices, and sometimes reporting requirements. An estimated operating hour is a disputable operating hour.
• Driving and rest times must be accurate to the minute. Anyone who relies on inaccurate data runs the risk of facing serious consequences during an inspection.
• Sector-specific tracking (e.g., in agriculture and contract work) requires reliable fuel and usage data for each machine and workday.

The common thread: as soon as data shifts from “useful” to “mandatory,” accuracy is no longer just a nice-to-have. It’s your burden of proof.

CAN bus data for the rental industry: one dashboard, all assets—even remotely

For rental companies, the challenge is shifting. Your equipment is rarely on your premises—it’s on your customer’s job site, sometimes hundreds of kilometers away, in the hands of someone you don’t manage. Yet you remain responsible for maintenance, and you’re the one who ends up footing the bill for damage that’s discovered too late.

That’s exactly where accurate CAN-bus data makes a difference—provided it’s all consolidated in one place. The rental company doesn’t want to read data from each device individually; it wants a single dashboard where all rented assets are immediately visible, regardless of where they are or who’s using them:

• Track remote maintenance based on actual operating hours—not on an estimate or the calendar. You make decisions based on data, without having to visit the site.
• Early detection of damage and malfunctions through error codes received directly while the device is still with the renter—not only after it is returned damaged.
• Objective evidence for billing: actual operating hours and usage as the basis for an accurate rental invoice and for substantiating damage.

For the rental sector, the dashboard isn't just a reporting screen—it's your control room for assets that you can't physically keep an eye on.

What to Look for When Choosing a CAN Bus Solution

These days, almost every supplier answers “yes” to the question “Do you have CAN bus data?” —which means that question hardly tells us anything anymore. The more relevant question is: “Does this value come directly from the vehicle, or is it calculated?” The difference lies in exactly what data, from which vehicles, with what level of accuracy, and how consistently it remains available within a mixed fleet.

Specifically, you should evaluate a solution based on the following points:

• Does the value come directly from the vehicle, or is it calculated? Ask this for each parameter—fuel, mileage, fuel economy—rather than as a single general question.
• How comprehensive is the vehicle and equipment coverage across the brands, models, and model years in your fleet, and does that data remain consistently available in a mixed fleet?
• Are the parameters you need —operating hours, PTO, error codes, load weight—being read, and not just the default values?
• Can the data be used as evidence for maintenance, rental, or legal registration?
• Do you get local support if something goes wrong? A data chain is only as strong as the support available when it breaks down.

Read more

FAQ

What does CAN bus mean?

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Fleet Management

CAN bus: What is it, and what are its applications?

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Legislation

Legislation Overview for Construction & Transportation

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